Process for the manufacture of aliphatic, olefinically unsaturated dicarboxylic acids



United States Patent Princess FOR THEMANUFACTURE or ALI- rnarrc,OLEFINICALLY UNSATURATED DICARBGXYLIC ACIDS 3,221,049 Patented Nov. 30,1965 tivity of the layers which first come into contact with the freshgas shall be somewhat lower than that of the following layers in thedirection of flow. By this step the temperature maximum is stronglyflattened and the tem- Wilhelm Riemenschneider, Ulrich Pintschovius, andOtto Wrature 1S substanflallif f umfonP Over the Whole Probst, Frankfurtam Main, Germany, assignors to dlstallce, whereby the yield 13 largelyImproved- Farbwerke Hoechst Aktiengesellschaft vormals Meister As t ys fd fi e ti s there can be used the Lucius & Briining, Frankfurt am Main,Germany, a following combinations: carroratiqn 0f Q Y (l) The individualcatalyst layers are distinguished j Flledflan; 1962 166,684 from oneanother by a different content of phosphoric Chums Gzermanyt 1961 acid.In the layer containing the largest proportion of 4 claims. phosphoricacid-the content of vanadium pentoxide always being the samethe reactionis attenuated to the The present invention relates to a process for thegreatest extentmanufacture of aliphatic, olefinically unsaturated dicar-15. The catalytically active ingredients are Used in boxylic acids.equal or similar composition, while different carrier ma- It is known toprepare aliphatic dicarboxylic acids, such 'Eerials are p y WhenOperating at i116 Same as maleic .acid, by catalytically oxidizinghydrocarbons perature, a catalyst applied to aluminum oxide as carrierhaving the same number of carbon atoms. As hydrocaris less active than acatalyst containing the same amount bons there are mainly used olefinsor di'olefins, i.e. butene 20 0f catalytically active SubstanceSupported on a kieselguhr and butadiene for the manufacture of maleicacid. In a i these processes the hydrocarbons are mixed with oxygen- (3)Catalysts having the same composition can be precontaining gases, suchas air, and conducted at elevated pared in diifcrent Ways. Theindividual components can temperature over an oxidation catalyst. Ascatalysts be simply mixed and shaped. Alternatively, vanadium there arementioned, above all, the oxides of vanadium pentoxide can be firstreacted with phosphoric acid. The and molybdenum, which are used invariable proportions compound obtained is then mixed with the carriermaterial with other metal oxides with the addition of phosphates andshaped bodies are formed. The catalyst obtained or phosphoric acid. Itis likewise known that catalysts without any reaction between vanadiumpentoxide and consisting of vanadium pentoxide and phosphoric acidphosphoric acid is the one having the lowest activity.

supported on inert carriers give favorable yields of di- (4) The stepsindicated sub (1)(3) can be combined, carboxylic acids in the reactionof olefinic hydrocarbons. i.e. catalysts can be used which diifer fromone another These good results are obtained, above all, when using in(a) the content of phosphoric acid, (b) the carrier a catalyst whichcontains the components vanadium pentmaterials and/ or (c) themanufacturing methods.

oxide and phosphoric acid in definite mixing proportions. As regards thestep illustrated sub (1) it has been found If in a contact tube thetemperatures of a fixed bed that the proportion of vanadium pentoxide tophosphoric catalyst are observed in the direction of flow, it is foundacid largely influences the working temperature of the that in mostcases the temperature rises steeply after a catalyst. The activity of acatalyst not only depends on certain heating distance. The temperatureincrease can the absolute amounts of active ingredients supported onamount to more than 100 C. even with the use of well the carrier, butalso to a decisive extent on the proportion cooled contact tubes. Such atemperature increase in a 0f the components. Thus it is possible tocontrol the contact tube in the direction of flow is undesired,temperature level of the oxidation so as to obtain optimum since at thepoints of high temperature side reactions may yields. The absoluteamounts of active ingredients and take place, for example formaldehydeand acetic acid the proportion of vanadium pentoxide to phosphoric acidmay be formed or the hydrocarbons may be burned to can vary withinrather wide limits. In the process of the carbon monoxide and carbondioxide. In a strongly invention the catalyst components are used in amolar exothermal reaction, as is the oxidation of olefins to diratio of1:05 to 1:3, calculated as V 0 and P 0 The carboxylic acids, thehydrocarbons may 'be substantially following table illustrates thereaction of 1.2% by volume converted into carbon dioxide and carbonmonoxide withof butene-l in admixture with 98.8% by volume of air on outnoticeable amounts of dicarboxylic acids being formed. catalysts havingdifferent compositions with a residence It has now been found that inthe manufacture 0f time on the catalyst of 0.3 second. Instead of airother aliphatic, olefinically unsaturated dicarboxylic acids from gasescontaining molecularoxygen or oxygen itself can be olefins and/ ordiolefins having 4 carbon atoms in a straight u d,

TABLE Carrier calcined H3P04 Maximum Temperature kieselguhr, V205, gramsgrams VgO5/P305 yield in percent at maximum grams of theory yield, C.

234 is 77 1 :2. 65 47. 5 500 234 28 92. 5 1:2. 04 45. 5 480 234 42 111.54 43. 0 460 234 as 1:1. 33 47. 0 440 234 100 178 1:1. 10 46. 5 430 234200 292 1:0. 90 44. s 420 chain with a catalyst containing vanadiumpentoxide, phosphoric acid and a carrier the aforesaid disadvantages canbe avoided when the reactor is not filled with a uniform catalyst butwith two or more zones or layers of catalysts having differentactivities. The catalytic ac- The mixing proportion of C hydrocarbons toair ranges from 1:99 to 1:49.

The table, which relates to the use of kieselguhr as carrier, revealsthat maximum yields can be obtained with 5 the most varying proportionsof vanadium pentoxide to in gradually and slowly.

phosphoric acid. When, for example, a catalyst is used which containslittle vanadium pentoxide, relatively large amounts of phosphoric acidmust be added in order to obtain good yields. If, however, a catalystcontaining a high proportion of vanadium pentoxide is used, aconsiderably smaller amount of phosphoric acid is required for obtainingthe same yields. The table likewise sh ws that the advantage of a highproportion of vanadium pentoxide resides in a strong reduction of theoxidation temperature.

The process of the invention is carried out at a temperature in therange from 350 to 550 C. and with a residence time on the catalyst of0.1 to 0.5 second. The above table only relates to kieselguhr as carriermaterial. Other carrier materials, such as aluminum, aluminum oxide,silica gel, porcelain, pumice, titanium dioxide, zirconium dioxide,silicon carbide or similar substances or mixtures thereof givefundamentally the same results, the numerical values, however, beingdifferent in each case.

Due to the higher content of phosphoric acid the layer in the reactorthat reacts first with the gaseous stream has a lower catalyticactivity. The oxidation reaction sets The subsequent zones in thereactor, which come into contact with the gas mixture that has partiallyreacted, are more active owing to their lower content of phosphoricacid. In these catalyst layers the reaction takes place until all theresidual hydrocarbon has been reacted.

Instead of using two layers the reactor can be filled with any number oflayers, or by suitable steps the reactor can be filled in a manner suchthat fillings with continuous transitions are obtained. In each case thereaction is retarded and the reaction heat evolved is distributed over agreater catalyst range. Consequently, the heat can be better dissipated,the yields are improved and the amounts of by-products formed arereduced.

The catalyst can be produced by mixing in various ways the threecomponents in the desired proportion. When a powdery carrier isemployed, it is necessary to shape the mixture, for example in anextruder or a tablet compressing machine. Alternatively, aqueoussolutions or suspensions of the active ingredients can be applied topreshaped carriers.

The dicarboxylic acids formed can be obtained either as anhydrides, forexample by directly cooling the reaction gases after they have left thereactor, or by washing them with an organic solvent, or when washingwith water in the form of aqueous solutions of the acids.

The process of the invention is suitable for oxidizing olefins ordiolefins having 4 carbon atoms in a straight chain to obtain thecorresponding olefinically unsaturated dicarboxylic acids or theanhydrides thereof. Thus butene-l, cis-butene-2, trans-butene-2,butadiene or mixtures of these substances can be oxidized, if desired inthe presence of isobutene, n-butane or isobutane, to yield maleic acid,or 2-methyl-butene-2 can be reacted to citraconic acid.

The following examples serve to illustrate the invention, but they arenot intended to limit it thereto.

Example 1 A vertical reactor consisting of a tube having an innerdiameter of 25 mm., surrounded by a thicker jacket tube through whichmercury was circulated, was filled with 1 liter of catalyst. A gasmixture was allowed to stream downward through the catalyst. The gasmixture was composed of 98.5% of air and 1.5% of a vaporized Chydrocarbon mixture consisting of 42% by volume of butadiene 18% byvolume of butene-1 7% by volume of trans-butene-Z 2.6% by volume ofcis-butene-2 7.4% by volume of n-butane 22% by volume of iso-butene 1%by volume of iso-butane Theoretically only 77% of the gaseous Chydrocarbons (sum of the straight chain C hydrocarbons) can contributeto the formation of maleic acid. The iso-compounds contained in themixture were oxidized to yield C and C hydrocarbons. Therefore, theyield was calculated on the utilizable 0., compounds only.

6.0 cubic meters of the reaction gas were used per hour, whichcorresponded to a residence time of 0.3 second at 390 C. The catalystwas heated to 390 C. by circulating the mercury under a pressure of 0.8atmosphere gauge. After having left the reactor, the reaction gases werewashed with water and thus freed from the maleic acid formed. The oilgas was either eliminated or wholly or partially re-used in the reactionafter having added fresh C gas mixture and, if necessary, air or oxygen.

(A) When the reactor was filled with 1 liter of a catalyst consisting ofI 234 grams of kieselguhr 42 grams of V 0 56 grams of H PO a yield ofmaleic acid of 47.2% was obtained.

(B) When 1 liter of a catalyst was used which consisted of 234 grams ofkieselguhr 42 grams of V 0 64 grams of H PO (85%) the yield of maleicacid amounted to 42.4%.

(C) When the reactor was filled with 1 liter of a catalyst consisting of234 grams of kieselguhr 42 grams of V 0 30 grams of H PO (85%) Example 2a yield of maleic acid of 39.0% was obtained.

(D) When the reactor was filled with three layers of catalyst, the lowerlayer consisting of /3 liter of the catalyst defined sub (A) the middlelayer consisting of /3 liter of the catalyst defined sub (B) and theupper layer consisting of /3 liter of the catalyst defined sub (C) ayield of 55.6% of maleic acid was obtained, calculated on the theory.

In the apparatus described in Example 1 a gas mixture of 1.2% by volumeof the C mixture defined in Example 1 and 98.8% by volume of air waspassed over a catalyst. The catalyst was heated by a diphenyl bath keptat the boil at 375 C. under a pressure of 7.2 atmospheres gauge. 1 literof catalyst was used consisting of 234 grams of kieselguhr 42 grams of V0 60 grams of H PO (85%) The yield of maleic acid amounted to 36%. Thetem perature peak in the interior of the catalyst was 500- 510 C. about40-50 cm. below the upper surface of the catalyst.

When, however, /2 liter of the last mentioned catalyst was filled in thelower part of the reactor and /2 liter of the catalyst defined inExample 1(A) there above and the gas mixture was allowed to flow throughthe whole catalyst under the conditions mentioned above, the yieldamounted to 52.3% of the theory.

Example 3 The experiment was carried out under the conditions set forthin Example 2 with the two-layer catalyst, with the exception thatinstead of 1.2% by volume of the l :3 C gas mixture defined in Example 1there was used the same amount of a C gas mixture consisting of 0.1% ofiso-butene 15.8% of n-butane 13.0% of trans-butene-Z 14.1% ofcis-butene-2 1.0% of butadiene 0.5% of isobutene 55.5% of butene-l Theyield amounted to 43.4 mol percent of maleic acid.

Example 4 The lower part of the apparatus defined in Example 1 wascharged with /2 liter of a catalyst obtained by reacting 28 grams ofvanadium pentoxide and 92 grams of phosphoric acid of 85% strength withspontaneous heating and mixing the cake obtained with 234 grams ofkieselguhr. The upper part of the reactor was filled with /2 liter of acatalyst which had the same composition but had been obtained by merelymixing all three components. When operating under the conditions setforth in Example 1, a yield of 54.5% of the theory was obtained. Whenusing the upper catalyst alone the yield amounted to 45.5%, while thelower catalyst alone gave a yield of 50.5%.

Example 5 The reactor described in Example 1 was filled in the lowerhalf with the catalyst defined in Example 4, which alone gave a yield of50.5% of the theory. The upper part of the tube was charged with acatalyst obtained by reacting 26 grams of vanadium pentoxide with 50grams of phosphoric acid of 85% strength with spontaneous heating andmixing the product obtained with 150 grams of aluminum oxide and 5 gramsof graphite, which catalyst when used alone gave a yield of 47%. Thereaction gases were conducted through both layers as described inExample 1 at a bath temperature of 400 C. The yield amounted to 53.2%.

We claim:

1. In the process for the manufacture of aliphatic olefinicallyunsaturated dicarboxylic acids by cont-acting molecular oxygen and anolefinic hydrocarbon selected from the group consisting of n-butenes,butadiene, and mixtures thereof, with a catalyst comprising vanadiumpentoxide, phosphoric acid, and an inorganic carrier, the improvement ofpassing a mixture of said molecular oxygen and said olefin over a bed ofsaid catalyst at a temperature of from 350 to 550 C. with a residencetime on the catalyst of from 0.1 to 0.5 second, the catalytic activityof said bed increasing in the direction of flow of the gas mixture.

2. A process according to claim 1, wherein the catalytic activity ofsaid bed is increased by decreasing the phosphoric acid to vanadiumpentoxide ratio in the catalyst in the direction of fiow of the gasmixture.

3. A process according to claim 2, wherein the phosphoric acid tovanadium pentoxide ratio decreases from 0.5 to 3.

4. A process according to claim 1, wherein the gases are passed throughtwo layers of catalyst, the second layer having an increased activity ascompared with the first one.

References Cited by the Examiner UNITED STATES PATENTS 4/1942 Pie 26066212/1956 Reid et al. 252-437

1. IN THE PROCESS FOR THE MANUFACTURE OF ALIPHATIC OLEFINICALLYUNSATURATED DICARBOXYLIC ACIDS BY CONTACTING MOLECULAR OXYGEN AND ANOLEFINIC HYDROCARBON SELECTED FROM THE GROUP CONSISTING OF N-BUTENES,BUTADIENE, AND MIXTURES THEREOF, WITH A CATALYST COMPRISING VANADIUMPENTOXIDE, PHOSPHORIC ACID, AND AN INORGANIC CARRIER, THE IMPROVEMENT OFPASSING A MIXTURE OF SAID MOLECULAR OXYGEN AND SAID OLEFIN OVER A BED OFSAID CATALYST AT A TEMPERATURE OF FROM 350* TO 500*C. WITH A RESIDENCETIME ON THE CATALYST OF FROM 0.1 TO 0.5 SECOND, THE CATALYSTIC ACTIVITYOF SAID BED INCREASING IN THE DIRECTION OF FLOW OF THE GAS MIXTURES.